Ribonucleic Acid RNA and Protein Synthesis Section 12

Ribonucleic Acid (RNA) and Protein Synthesis Section 12 -3

Outline of today’s information Translation RNA - basics 1 2 Transcription 3 Summary 4 Replication 5

Outline of today’s information RNA - basics 1 2 3 4 5

The DNA/RNA connection DNA and RNA are partners in the business of making proteins. DNA is a specialist. It provides stable, permanent storage of the code (or recipe) for making proteins RNA is a generalist (more versatile). It serves a variety of roles (including the “chef”) to make (synthesize) proteins.

Structure of RNA (ribonucleic acid) *Notice the differences (in red) from DNA* A long chain of nucleotides p SINGLE stranded p Phosphate, sugar (ribose), nitrogenous base p n Adenine, guanine, cytosine, URACIL

3 Types of RNA p messenger RNA (m. RNA) n p ribosomal RNA (r. RNA) n p Instructions for assembling proteins out of amino acids – code is copied from DNA and taken to the rest of the cell. The main pieces that make up ribosomes (along with some protein components). Ribosomes assemble proteins. transfer RNA (t. RNA) n Transfers (delivers) amino acids to ribosomes.

Checkpoint p What are three differences between RNA and DNA? p What are three types of RNA? p What does each kind of RNA do?

RNA makes proteins from the information stored in the cell’s nucleus (DNA). This requires two different processes — transcription and translation. process types of RNA involved location function transcription messenger RNA m. RNA nucleus copy DNA translation messenger RNA m. RNA On a ribosome in the cytoplasm make proteins transfer RNA t. RNA ribosomal RNA r. RNA

Outline of today’s information RNA - basics 1 2 Transcription 3 4 5

Transcription - the conversion of information from one form to another. In molecular genetics, transcription is when the “code” found in DNA is transcribed (or copied) into a complementary sequence of RNA.

Cooking/Kitchen analogy of transcription of DNA into RNA If DNA is like a treasured cookbook in your grandmother’s house that is filled with dozens of family recipes, p Then, the process of transcription is like copying down one recipe from Grandmother’s cookbook (let’s say, pecan pie) onto an index card that you can take home to use. p The m. RNA is the “index card with one copied recipe. ” p

A brief description of transcription The enzyme RNA polymerase binds to a particular part of the DNA that says “the gene starts here. ” 1. • This location is called the promoter site. RNA polymerase - the enzyme that makes an RNA copy of the DNA gene

A brief description of transcription After the RNA polymerase binds to the promoter site, the 2 strands of the DNA begin to unzip to form a “bubble” of unpaired DNA strands. 2. • This allows space for the m. RNA to be assembled. RNA polymerase - the enzyme that makes an RNA copy of the DNA gene

A brief description of transcription The m. RNA transcript is built nucleotide by the RNA polymerase as it moves over the DNA (gene). 3. • The assembled RNA nucleotides are complementary to the nucleotides on the DNA. RNA polymerase transcribing the gene

RNA/DNA base-pairing rules (for making the m. RNA) Complementary nucleotides In the new strand of RNA, ______ pairs With _____ on the DNA template Guanine (G) Cytosine (C) Guanine (G) Adenine (A) Thymine (T) Uracil (U) Adenine (A)

Example of base-pairing What would the m. RNA sequence be if the DNA template strand were: p ATTGGCGCTAAC ? p

A brief description of transcription 4. The end of transcription occurs when • the end of the gene is reached • the m. RNA is cut loose • the m. RNA is edited (in eukaryotes) to make it ready for use • the m. RNA is exported out of the nucleus and into the cytoplasm. RNA polymerase transcribing the gene

Checkpoint If the DNA sequence is: ATT GTC CAC TGG AGC What will the m. RNA be after transcription?

Can you now describe what is going on in this picture? nucleus m. RNA polymerase DNA

Outline of today’s information Translation RNA - basics 1 2 Transcription 3 4 5

Translation p m. RNA (messenger RNA) is DECODED by a RIBOSOME to make… Proteins

p m. RNA attaches to a ribosome p m. RNA is read 3 bases at a time by the ribosome. p This three-base unit is called a codon. Translatio n

p As each codon (3 N-bases) moves through the ribosome like a ribbon… p The t. RNAs with the correct anticodon bring the required amino acids. n (continued)

Translation p Anticodon - the 3 -base sequence on each different t. RNA that is complementary to a codon on m. RNA. (codon) From Wikipedia commons

The relationship between t. RNAs and amino acids p Each amino acid (a. a. ) is carried by t. RNAs that have anticodons complementary to the m. RNA codons. p We will look at how this genetic code works a little later.

Translation q The ribosome forms a peptide bond between ribosome this newly delivered amino acid and the previous a. a. in the chain. q This makes the polypeptide chain (what will be the protein) one a. a. longer.

Translation q t. RNA (minus its amino acid) is released q The ribosome moves to next codon q This continues until a Stop Codon is reached q New polypeptide is released ribosome

Can you now describe what is going on in this picture?

Proteins The whole purpose of the genetic code is to assemble complicated proteins perfectly, over and over, millions of times. p Proteins (polypeptides) are long chains of amino acids (20 different ones) that are connected in a specific order. s. How can just four “letters” (the four Nbases in RNA) code for the correct amino acid (if there are 20 different ones)? p s. A, U, C, G vs. 20 different amino acids?

Proteins § RNA is read 3 letters at a time § Like “ 3 letter words” § These 3 letter words are called codons. § Examples § AUG § GGC § UUA

Cracking the Code m. RNA UCGCACGGU p p Codons: UCG CAC GGU

Translation p p p These strings of codons are then translated into proteins by the interaction of ribosomes and t. RNA’s only deliver their specific amino acid to the ribosome when the m. RNA has the appropriate complementary codon. We can use a chart to determine which amino acids are coded for by a given codon.

Codons: UCG CAC GGU Note the 20 amino acids plus the 3 stop codons

Proteins p Example: n n n If a DNA sequence is GGCTATCTA, The complementary m. RNA sequence is… CCG AUA GAU Using a genetic code chart (like on pg. 303), one can determine that these three codons correspond to the following amino acids: Proline Isoleucine Aspartic Acid

Checkpoint If the DNA sequence is: GTAGGCCTCTGGTGCACT What will the m. RNA be after transcription? What will the amino sequence be?

Outline of today’s information Translation RNA - basics 1 2 Transcription 3 4 Replication 5

DNA transcription and translation compared with DNA replication p DNA transcription and translation n p One small gene at a time Nearly constant throughout cell’s life For assembling the proteins of which we, and all living things, are made. DNA replication n Requires the copying of the cell’s entire collection of DNA. Is only performed once in the cell’s life. For reproduction where all the instructions for making an organism must be passed on.

Outline of today’s information Translation RNA - basics 1 2 Transcription 3 Summary 4 Replication 5

Central Dogma of Molecular Biology transcription replication DNA RNA translation Protein

Summary Checkpoint What does each type of RNA do? Describe what happens in transcription. Describe the process of translation. Beginning with a DNA sequence, you need to be able to figure out the amino acid sequence it codes for. If the DNA sequence is TGAGGGAGA…

Mutations Cells do rarely make mistakes copying their own DNA resulting in a change in the DNA. p Mutation – a change in genetic material. p Types of mutations p n n Gene mutations – mutations that produce changes in a single gene. Chromosomal Mutations p Changes in the number or structure of chromosomes.

Results of mutations Can be very harmful p Can be neutral (neither harmful nor good) p Also result in genetic variability p n p Good for changing environments Plant and Animal Breeders n n Polyploidy = extra sets of chromosomes (3 N, 4 N, 6 n, 8 n, 10 n, etc. ) Bananas, citrus fruits, seedless fruit

Protein synthesis animations p http: //www. stolaf. edu/people/giannini/flas hanimat/molgenetics/transcription. swf p http: //www. stolaf. edu/people/giannini/flas hanimat/molgenetics/translation. swf p http: //student. ccbcmd. edu/~gkaiser/biotu torials/protsyn/translat. html

Protein synthesis animations http: //wwwclass. unl. edu/biochem/gp 2/m_biology/ani mation/gene_a 1. html p http: //wwwclass. unl. edu/biochem/gp 2/m_biology/ani mation/gene_a 2. html p http: //wwwclass. unl. edu/biochem/gp 2/m_biology/ani mation/gene_a 3. html p

p http: //student. ccbcmd. edu/~gkaiser/biotu torials/protsyn/translat. html p http: //wwwclass. unl. edu/biochem/gp 2/m_biology/ani mation/gene_a 3. html

http: //www. biostudio. com/demo_freeman _protein_synthesis. htm p http: //www. wisconline. com/objects/index_tj. asp? obj. ID=AP 1302 p http: //www. abdn. ac. uk/~clt 011/flash/sam ples/protein. swf p